Conventional computing devices enable a user to input a choice or a selection in different ways. For example, a user can use an alphanumeric keyboard, a cursor control device or a microphone to indicate a choice or selection. Moreover, touch sensing technology can be used to provide an input selection to a computing device or other types of electronic devices. Within the broad category of touch sensing technology there exist capacitance sensing touch sensors, commonly referred to as touchpads.
A capacitance sensing apparatus can include a number of capacitance sensor elements (e.g., wires) underlying a sensing region. If an object such as a user's finger is in proximity to (or in contact with) the sensing region, a capacitance is induced in one or more of the capacitance sensor elements, generating a signal. The capacitance sensor elements are coupled to sensor circuitry (e.g., an integrated circuit), which interprets signals received from the capacitance sensor elements.
The sensed position of a finger or object relative to the touchpad should be unambiguous. That is, for example, the response of the sensing apparatus to a finger at any location in the sensing region of the capacitance sensing apparatus should be different from the response at other locations on the touch sensor.
The accuracy to which a position within the sensing region can be determined is influenced by the number of capacitance sensor elements underlying the sensing region. For example, the granularity of the sensing region can be increased by increasing the number and hence the density of capacitance sensor elements. Increasing the number of capacitance sensor elements can also improve signal-to-noise ratios.
If a greater number of capacitance sensor elements are used, then an integrated circuit coupled to those sensor elements would appear to need more inputs or channels. Consequently, costs associated with the sensor circuitry may be increased. Furthermore, commercially available (e.g., “off the shelf”) integrated circuits may not have enough inputs to accommodate a large number of capacitance sensor elements. Hence, either the number of capacitance sensor elements is constrained by the number of inputs on existing integrated circuits, or specialized integrated circuits designed with a larger number of inputs are needed.
Accordingly, a capacitance sensing apparatus that can be used to accurately indicate the position of an object or finger, but that avoids the design and cost issues mentioned above, would be advantageous.